Actividad reproductiva y longitud de madurez de sardina austral Sprattus fuegensis en el mar interior de Chiloé, Chile Reproductive activity and maturity length of Patagonian sprat Sprattus fuegensis in Chiloé inland seawaters, Chile

The Patagonian sprat, Sprattus fuegensis, has been recently identified in the catches of small pelagic fish in the inland waters of Chiloe, southern Chile. In spite of its increasing economic importance, there are still unknown aspects of its reproductive biology. This study describes the reproductive activity of females of this species based on monthly variation of the Gonadosomatic Index (IGS) and the frequency of macroscopic states of maturity between January of 2006 and December of 2009 and microscopic states since February of 2007. The maturity at length of females was studied during the main spawning season. IGS monthly variation and the frequency of macroscopic states of maturity reached maximum values each year, between September and October, and minimum from January to June. In addition, the histological analysis of the ovaries confirmed that S. fueguensis is a partial spawner whose reproductive activity although tends to concentrate between September and October can be extended to December. The mean length at maturity of females during the reproductive season was 13.5 cm, indicating that they spawned at longer lengths in comparison with the same species from other localities. It is discussed that the increase of the reproductive activity in spring and larger maturity sizes could be part of a reproductive strategy of the species to enhance the survival during early stages in the inland seawater of Chiloe.